David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Christina Howard, Produce Safety Professional

Male and Female Spotted Wing Drosophila
Male and Female Spotted Wing Drosophila; image by Alan Kenage, Capital Press. Used with permission.

Click on photos to enlarge.

Spotted wing drosophila (SWD) fruit fly numbers continue to increase at nearly all of the sites that we are monitoring. Trap counts this week are mostly well above levels considered damaging to ripening berry crops, especially raspberries and blueberries (see table below). Sites capturing more than four SWD flies in a week should remain on a protective spray schedule to prevent fruit from becoming infested with larvae. A seven-day spray interval should still be adequate in most situations, but a five day interval may become necessary if larvae continue to be present in fruit with the seven day interval. Be sure to read and follow all pesticide product labels carefully, especially in regards to days to harvest restrictions and the number of applications allowed per growing season. Rotate products used regularly to prevent the possible development of resistance.

We expect populations to increase further in the coming weeks as more food (fruit) becomes available for the flies, especially if conditions remain warm and humid. Remember that keeping the field free of waste fruit can significantly reduce drosophila numbers. Apply protective sprays on any berries that have begun to ripen, when more than four spotted wing drosophila flies are caught in a trap, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay. The flies are most prevalent in the lower, shaded parts of the plants.

Drosophila Trap
Drosophila Trap, photo by David Handley


Current information on registered pesticides for managing SWD is available in the New England Small Fruit Management Guide.  The online version is free and can be viewed here 

For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit our SWD blog

Other IPM Web Pages
Michigan State University

Penn State University

University of New Hampshire


David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                       Pest Management Unit
P.O. Box 179                            17 Godfrey Drive
Monmouth, ME 04259           Orono, ME 04473
207.933.2100                           1.800.287.0279

Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

Spotted Wing Drosophila Weekly Trap Captures in Yeast/Vinegar Traps

Town Spotted Wing  Drosophila weekly trap catch 7/17/20 Spotted Wing  Drosophila weekly trap catch 7/24/20 Spotted Wing  Drosophila weekly trap catch 7/31/20
Wells 8 21 3
Sanford 0 2 40
Limington 2 8 115
Limerick 24
Cape Elizabeth 1 121
Bowdoinham 18 371 750
Mechanic Falls 0 0
Monmouth 5 15 100
Wayne 13 36